most hard disks are fixed hard disks, which are permanently sealed and fixed in the hard disk drive. Early hard disk storage media were replaceable, but today's typical hard disk is a fixed storage media, which is sealed in the hard disk (except for a filter hole to balance air pressure). With the development, removable hard disks have appeared, and become more and more popular, with more and more types. Most hard disks installed on microcomputers are called "winchester hard disks" or "warm disks" for short because they all adopt winchester technology.